Just one more thing
I have not used a kindle 4so I can't compare it.
The Kobo mini, because of its whiter screen enables me to read at much smaller fonts with much weaker reading glasses. Thus more on the page and better formatting options overall.
The Kobo Glo with its bigger screen and higher resolutions should be much better. I know it costs more, but I would advise you to at least look at one before purchasing. The Kobo Mini at $79 CAD is much better to read on than the T1 which I believe has as good as or possibly better screen than K4 and the Glo should be even better.
The Glo at $129 CAD may be more than you want to pay, but looking at the price over a year it is about 30 cents a day and while not perfect it is about as good as it gets.
Plus you can download library books for it in in far more countries than a kindle.
Still I am pretty sure you will be happy with the K4 as well so happy ereading.